Radio frequency switch



. sept. 17, 1946. 11m/PETERSON 2,407,847

R. F. SWITCH Filed May l, 1945 Patented Sept. 17, 1946 RADIO FREQUENCYSWITCH Donald W. Peterson, Princeton, N. J., assignor` to RadioCorporation of America, a corporation of Delaware Application May 1,1943, Serial No. 485,388

This invention relates to radio-frequency switches, such as are used formaking and breaking electively connections between radio frequencysources and loads, reversing or changing the phases of the currentsflowing in various parts of radio frequency circuits, and the like.

Such switching and phasing functions are required for example in theoperation of directive antenna systems when a plurality of directivepatterns are to be provided selectively. It is com-mon practice toemploy various combinations of variable capacitors and transmission linesections for these purposes. `For example, if two points in a radiofrequency circuit are to be alternately connected together anddisconnected, a capacitor capable of being varied between two valuesCmin and Cmax is coupled to the two points through a transmission line.The line is of such length that the reactance o1 the capacitor atone ofits settings, for example, Cinex is transformed to a short circuit atthe end of the line. The reactance presented at the end of the line byCmin is tuned to parallel resonance by a stub line or a similar reactiveelement, so as to produce an open circuit. Thus, by changing thecapacitance from Cmax to Cmin or vice versa, a short circuit or opencircuit may be provided. Similar arrangements are used for phaseshifting or phase reversal in radio frequency networks.

' Although radio frequency switching systems of the above described typecan be made highly effective by careful design, the variabl-e capacitorsare relatively bulky and expensive. Also, the transmission line networksnecessary to achieve the desired operations may be somewhat compleX.Accordingly, it is the principal object of the present invention toprovide an improved method of and means for controlling the ilow ofradio frequency currents.

Another object of the invention is to provide an improved radiofrequency switch structure comprising a minimum of moving parts andrequiring no close mechanical tolerances.

A further object is to provide an improved radio frequency switchstructure which is readily adaptable to remote control. These and otherobjects will become apparent to those skilled in the art uponconsideration of the following description with reference to theaccompanying drawing, in which Figs. l and 2 are sectional schematicdiagrams of switches constructed in accordance with the invention andFig. 3 is a schematic diagram of a typical network including the switchof Fig. 2.

Referring t0v Fig. 1, a concentric transmission 6 Claims. (Cl. 178-44)line l is to be selectively short circuited and open circuited betweenthe inner conductor 3 at a point 5 and the outer conductor l'. A tubularconductive member 9 is connected to the outer conductor l' of the line Iand extends substantially at right angles thereto. A second tubularconductive member II is supported concentrically within the conductor 9and connected to the point 5 on the inner conductor 3 of the line I. Thespace between the walls of the tubular members 9 and I I may be filledWith insulating material it, such as hard rubber, polystyrene, or thelike. The insulator I3 extends beyond the end of the member I I and isprovided `with a cylindrical bore concentric with and substantially ofthe same diameter as that of the member II. The length of the member I!is onequarter electrical wavelength at the frequency at which the systemis to operate.

An iron rod I5, insulated by a coating I1 of polystyrene or the like, isprovided within the bore of the member I3 and is adapted to movelongitudinally therein between the positions shown in Fig. 1 and Fig. 2.A winding I9 is provided on the outside of the member 9 at the endadjacent to line l. The winding i9V is connected through a switch 2l ltoan electrical source'23 such as a generator. The rod I5 is substantiallyone-half wavelength long so that when itis in the position shown in Fig.2 it extends substam tially one-quarter electrical wavelength beyond theend of thetubulai` member iI. The operation of the above describedstructure is as follows: I

When the parts are in the position illustrated in Fig. 1 the tubularmembers 9 and I I cooperate to function as a quarter wave lineopen-circuited at one end and connected across the line I at the otherend. Owing to the well known impedance inversion characteristics ofquarterwave lines the open circuit at the far end of this line isreflected as a short circuit between the point 5 and the outer conductorl. When switch 2| is closed the solenoid winding i8 is energized,

drawing the iron rod I5 into the position shown l in dot and dash lines.Since the rod I5 and the tubular member II overlap for substantially aquarter wavelength they present the electrical characteristics of asingle conductor one-half wavelength long. Thus, the members 9, I I andI5 together constitute a half wavelength line open-circuited at its farend and present an open circuit between the point 5 and the outerconductor 1 To retract the member `I5 from the member II a secondsolenoid mayI be provided Afrequency line.

at the outer end of the member 9 or the device may be mounted in such aposition that gravity will effect a withdrawal when the switch 2| isopened. If desired, the rod I may be magnetically polarized, and thecoil I9 energized from a D.-C. source through a reversing switch.

Fig. 2 showga modification of the switch of Fig. 1 arranged to shortcircuit and open circuit selectively two transmission lines I and I. Theouter conductor 9 is connected between the outer conductors I and I. Theinner tubular conductor I I is duplicated with a conductor II connectedto the inner conductor of the line I. A solenoid I9' surrounds the outerconductor 9 at the end adjacent the line I. The windings I9 and I9 areconnected through a double throw switch 2| to the source 23. A singlerod member I5 is provided as in the structure of Fig. 1. When the switch2| is thrown to -the left, the rod I5 is drawn into the tubular member|I, short circuiting the line I at the point 5. When the switch 2|' isthrown to the right, ythe rod I5 is drawn into the tubular member Il',short circuiting the line I at the point 5 and presenting an opencircuit across the line I.

Fig. 3 Vshows the above described switch arranged to reverse the phaseon a balanced radio Conductors 25 and 2'! constitute a parallelopen-wire transmission line, balanced with respect to ground. Juxtaposedpoints 29 and 3| on the lines 25 -and 2'! respectively areinterconnected by a concentric line S5 one-half electrical wavelengthlong. A point 3l one-quarter wavelength to the left of point 29 isconnected to the point 39 one-quarter wavelength to the right of thepoint 3| by a half-wave line 4|. The point 43 one-quarter wavelength tothe left of the point 3| is similarly connected to the point 45one-quarter wavelength to the right of the line 29 by a half wave line41. The mid points 5| and 53 of the lines 4| and 4'! respectively areconnected together by a half-wave line 49. A switch 55A is connectedbetween the points 29 and 5I. The switch 55 may comprise a structuresimilar to that of Fig. 2 arranged to provide a short circuit at one endat the same time as an open circuit is presented at the other end. Theoperation of the system of Fig. 3 is as follows:

VAssume that the switch 55 is actuated so that the point 29 isshort-circuited while the point 5i is open-circuited. The short circuitat the point 29 is reected as an open circuit at the points 31 and Theopen circuit at the point 5I has no effect upon the performance of theline 4I. Thus, the short circuit presented at the point 29 reflects ashort circuit at the point 3| through the half wave line 35. The shortcircuit at the point 3| is reiiected at the points 39 and 43 as opencircuits. Energy applied to the line 25 flows from the point 31 throughthe line 4I to the point 39 and energy applied to the line 2 lflowsthrough the line 4l to the point 45. Thus the polarities of the points39 and 45 are reverse with respect to the corresponding points 43 and.31. When the switch 55 is actuated so as to provide a short circuit atthe point 5Il and an open circuit at the point 29, open circuits arepresented at the points 31 and 39 by the line 4| and at points 43 and 45by the line 4'I. Energy applied through the lines 25 and 21 to thepoints 45 and 39 directly through points 29 and 3| and the polarity ofthe point 45 with respect to that of point 39 is the same as thepolarity of the point 3'I with respect to that of `point 43.

Although only one application of the invention has been specificallydescribed it will be apparent that its utility is not limited thereto.For example, it will be clear without further illustration that switchesof the described type may be employed to insert or remove line sectionsof undesired length in a transmision line circuit for providingdifferent phase shifts between predetermined points. It should also benoted that although the illustrated embodiment is arranged to beoperated electro-magnetically, the outer conductor 9 may be slotted toprovide for mechanical operation by means of a pin or the like'extending radially from the member I5. In the case of a single endedstructure such as that of Fig. 'l the member I5 may be provided with anextension rod of insulating material for mechanical operation throughthe outer end of the switch structure.

The invention covered herein may be manufactured and used by or for theGovernment of the United States for governmental, military, naval andnational defense purposes without payment to me or assigns of anyroyalty thereon.

I claim as my invention:

l. A system for selectively presenting an open circuit and a shortcircuit between two predetermined points in a radio frequencytransmission system, comprising a tubular member of conductive materialconnected to one of said points, a second tubular conductive memberconnected to the other of said points and positioned. within and coaxialwith said first tubular member, and an insulated rod of conductivematerial adapted to move longitudinally within said second tubularmember.

2. A system for selectively presenting an open circuit and a shortcircuit between two predetermined points in a radio frequencytransmission system, comprising a tubular member of conductive materialconnected to one of said points, a second tubular conductive memberconnected to the other of said points and positioned within and coaxialwith said first tubular member, an insulated rod of conductive magneticmaterial adapted to move longitudinally within said second tubularmember, and solenoid means supported on the outer surface of said firsttubular member.

cluding a body of insulated material positioned between the inner wallof said first tubular member and the outer wall of said second tubularmember,

4. The invention as set forth in claim 1 wherein said second tubularmember is substantially 1A, electrical wave length long and said rodmember is substantially 1/2 electrical wave length long.

5. A radio frequency distributioncircuit, including an open wire,transmission line comprising two conductors, a concentric line 1/2 wavelength long connected between juxtaposed points on said conductors,second and third concentric lines each 1/2 wave length longcross-connected between points on said first and second conductors 1/4wave length to each side of said juxtaposed points, a fourth concentricline 1/2 wave length long connected between the midpoints of said secondand third lines, means for alternately providing a short circuit and anopen circuit at one of said midpoints, and means for simultaneouslyproviding respectively an ope-n circuit and a short circuit at one ofsaidjuxtaposed points, said last named means comprising Y 6. Theinvention as set forth in claim 5 Wherein said rod member is made ofmagnetic material and said outer tubular member is surrounded by electromagnet means comprising at least 5 one solenoid Winding.

DONALD W. PETERSON.

